Lung injury causes excessive pulmonary artery smooth muscle cell (PASMC) proliferation in the peripheral arteries of the lung and pulmonary hypertension and significant morbidity in infants and children. Laboratory studies indicate that inhaled nitric oxide (NO) attenuates pulmonary vascular disease in the developing lung. Although the protective mechanisms of NO are incompletely understood, NO regulates PASMC in part by stimulating soluble guanylate cyclase to synthesize cGMP, which stimulates cGMP-dependent protein kinase (PKG). PKG has been observed to induce PASMC differentiation by decreasing cell proliferation, increasing the expression of contractile proteins, and stimulating apoptosis. The BROAD, LONG-TERM OBJECTIVES of this grant proposal are to identify and characterize molecular mechanisms whereby PKG regulates PASMC differentiation. Recently, we identified two novel RING finger proteins, TRIM39R and axotrophin (AXOT), that interact with PKG in a yeast two-hybrid assay. Since PKG and RING finger proteins both regulate cell differentiation, they may share similar signaling pathways and RING finger proteins may mediate many of the cell regulatory activities of PKG. The central hypothesis of the proposal is that PKG regulates PASMC differentiation by interacting with RING finger proteins and regulatory proteins. Specific aim 1 examines how TRIM39R modulates PKG's regulation of PASMC proliferation, differentiation, and apoptosis. Specific aim 2 defines the molecular interaction between PKG and AXOT and defines the role of AXOT in modulating PKG's important non-vasodilatory actions in PASMC. Specific aim 3 utilizes a novel experimental approach to identify new RING finger and transcription regulating proteins phosphorylated by PKG in PASMC, based on their differential phosphorylation in cells. The studies proposed in this grant application will provide important new mechanistic information about how PKG modulates PASMC proliferation, differentiation, and apoptosis. They are likely to provide information that will lead to the development of novel therapeutic targets that can be used to prevent pulmonary vascular disease in the injured lung. [unreadable] [unreadable] [unreadable] [unreadable]